1. Field of the Invention
The present invention relates to a multi-laminated inductor used for various circuits and a manufacturing method and more particularly to a multi-laminated inductor comprised of laminated internal conductors forming a coil along the length of the chip.
2. Description of the Related Art
Conventional multi-laminated inductors are classified into two broad categories in the relation between the direction of laminating internal conductors and the outside shape of the chip, which form the coil. For example, multi-laminated chip inductors have such a structure that coil-shaped internal conductors made of silver or silver-palladium alloy are contained in a nonconductor material or ferrite magnetic material and both ends of the coil are connected to external terminal conductors respectively.
FIG. 2 shows a relation between the direction of laminating internal conductors and the outside shape of the chip in this type of multi-laminated chip inductors. It has one structure that the internal conductors 2 are laminated along the thickness Lt (or width Lw) of the multi-laminated chip inductor 1. Usual multi-laminated chip inductors have this structure. Here, the both ends of a coil-shaped conductor are connected to external terminal conductors 3a and 3b, respectively.
On the other hand, Japanese Patent Application Laid-Open No. 8-55726 teaches the another structure of a multi-laminated chip inductor 6 as shown in FIG. 3. That is, internal conductors 4 are laminated along the length L1 of the chip 6 and are external terminal conductors 5a and 5b formed at both end portions along its length.
This structure is generally referred to as a longitudinal stack type, and has features that it can provide relatively high inductance values and high self-resonance frequencies.
multi-laminated chip inductor of the longitudinal stack type, which has been developed applicant""s assignee and is of a type disclosed in the co-pending, commonly assigned Ohno et al application, Ser. No. 09/240,699, filed Feb. 2, 1999, now U.S. Pat. No. 6,304,164, has a laminated structure as shown in FIG. 4, for example. That is, a coil is formed by laminating a plurality of magnetic material sheets 7a and 7b having internal conductor patterns 4a and 4b shaped like a letter L thereon, and then connecting the internal conductors 4a and 4b through via holes 8a and 8b into the shape of a spiral. Further, both ends of the coil formed by the internal conductor patterns 4a and 4b are connected to via holes 8c and 8d formed in a plurality of laminated magnetic material sheets 7c and 7d, respectively.
Thereby, lead conductor portions are formed by coupling a plurality of via holes 8c and 8d. The via holes 8c and 8d exposed to the surfaces of the magnetic material sheets 7c and 7d placed at both ends are connected to the external terminal electrodes 5a and 5b. These external terminal conductors 5a and 5b are formed on the both end faces along the length of the chip and on portions of the faces adjacent to these end faces.
In the conventional multi-laminated chip inductors 6 of the longitudinal stack type described above, the external terminal electrodes 5a and 5b are formed on both end faces along the chip length in which are perpendicular to the winding center-line of the coil formed by internal conductors 4.
Therefore, when the magnetic flux generated by the passage of electric current through the coil passes through the external terminal electrodes 5a and 5b, eddy current is generated within the external terminal electrodes 5a and 5b. This eddy current has been one of the factors that increase its electrical loss.
Further, as the internal conductors 4 and the external terminal electrodes 5a and 5b are disposed nearly parallel to each other, stray capacity is produced between them. This stray capacity has been one of the factors behind a reduction in the self-resonance frequency of the inductors.
Also, in manufacturing of multi-laminated chip inductors of the longitudinal stack type described above, there has been no approach for adjusting a value of inductance except re-designs such as changing the core area. It has been also necessary to change the content of design for each different value of inductance. Thus, the control of design specification has been very complex.
Considering the problems described above, it is an objection of the present invention to provide a multi-laminated inductor and a method for manufacturing it which allow reducing eddy current generated within an external terminal electrode and further an easy adjustment/modification of a value of inductance.
In order to achieve the objective described above, by providing a lead layer having a lead internal conductor exposed to a chip surface nearly parallel to the winding center-line of a coil and connected to an end of the coil for a predetermined layer, and forming an external terminal electrode formed on a face nearly parallel to the winding center-line of the coil and connected to the lead internal conductor, a multi-laminated inductor having the chip with a laminated structure having the coil buried therein and the external terminal electrode formed on the chip surface and connected to the coil is configured.
According to this multi-laminated inductor, the external terminal electrodes are formed on the faces parallel to the winding center-line of a coil, so that the magnetic flux generated by the passage of electric current through the coil does not intersect the external terminal electrodes surface. Thus, eddy current within the external terminal electrodes is prevented from generating, and so increasing the loss generated by the eddy current can be suppressed.
Also, by providing a lead internal conductor exposed to all the faces parallel to the winding center-line of a coil, it is not necessary to select a face having the external terminal electrode exposed therein at the production of the coil, so that the manufacturing process can be simplified.
Also, according to the invention , the multi-laminated inductor described above is provided with a chip shaped like a rectangular solid which has square-shaped insulating material sheets laminated therein and further provided with a lead layer comprising an insulating material sheet having a first lead internal conductor formed thereon and an insulating sheet having a second lead internal conductor formed thereon; wherein the first lead internal conductor is formed like a cross shape with a predetermined width and has its intersection point at the center of the insulating material sheet and their four edges reach to the four edges of the insulating material, and the second lead internal conductor is formed like a linear shape with a predetermined width and placed so that one end thereof is connected to the first lead internal conductor nearly at the center of the insulating material sheet and the other end thereof is connected to a predetermined spot of the end of the coil.
According to this multi-laminated inductor, the coil and the external terminal electrode are electrically connected by means of the first and second lead internal conductors. Since these first and second lead conductors are formed like a cross and linear shape respectively, the area intersecting the magnetic flux generated by the coil can minimized, and so eddy current within the first and second internal conductors can be prevented from generating.
Further, the chip is shaped like a rectangular solid and the insulating material sheets are shaped like a square, and further the first lead internal conductor is exposed to the four surfaces of the chip which are parallel to the winding center-line of the coil. Therefore, even when the external terminal electrode is formed on any face of the four surfaces, the same multi-laminated inductor may be obtained. Further, by forming a second lead internal conductor at varied position in the production of the coil, the position of connection between the second lead internal conductor and an end portion of the coil can be changed. Thus, the value of inductance can be easily changed.
Also, according to the invention, the multi-laminated inductor described above is provided with a rectangular solid-shaped chip having square-shaped sheets of insulating material laminated and further provided with a lead layer made of an insulating material sheet having a first lead internal conductor formed thereon and an insulating sheet having a second lead internal conductor formed thereon, wherein the first lead internal conductor is formed along a diagonal of the insulating material sheet and both ends thereof each are formed like a linear shape with a predetermined width extending over two sides, the second lead internal conductor being formed like a linear shape with a predetermined width and being placed so that one end thereof may be connected to the first lead internal conductor nearly at the center of the insulating material sheet and the other end thereof may be connected to a predetermined spot of the end of the coil.
This multi-laminated inductor has the first and second lead internal conductors establishing an electrical connection between an end of the coil and an external terminal electrode. Since these first and second lead internal conductors are formed like a linear shape, the area intersecting the magnetic flux generated by the coil can be minimized. Thus, Eddy current can be prevented from generating within the first and second lead internal conductor. Also, the chip is shaped like a rectangular solid and the insulating material sheets are shaped like a square, and the first lead internal conductor is exposed to the four chip surfaces parallel to the winding center-line of the coil. Therefore, even when the external terminal electrode is formed on any one of the four surfaces, the same multi-laminated inductor can be obtained. Further, by forming the second lead internal conductor at a varied position in the manufacturing, the second lead internal conductor can be connected to the varied end of the coil. Thus, the value of inductance can be easily varied.
Also, according to the invention, in the multi-laminated inductor described above, the external terminal electrodes are disposed at both end portions along the winding center-line and portions thereof are continuously spread over the peripheries of the adjoining faces.
As this multi-laminated inductor can provide a long distance between two external terminal electrodes, when mounted on a board it can reduce the stress produced at the external terminal electrodes due to the bending of the board. Thus, the occurrence of connection failure between the electrodes on the board and the external terminal electrodes can be reduced.
Further, according to the invention, the multi-laminated inductor described above is provided with the external terminal electrodes formed on both end portions, along the winding center-line of a coil, in each of the two faces nearly parallel to the winding center-line of the coil and adjacent to the face which are opposed to a board surface when mounted on the board and parallel to an orbital centerline of the coil.
This multi-laminated inductor can provide a long distance between the external terminal electrodes which are formed on both end portions along the winding center-line of the coil. Therefore, when the inductor is mounted on a board, the stress produced at the external terminal electrodes due to the bending of the board can be reduced. Further, the multi-laminated inductor allows to be mounted on a board so that the external terminal electrodes may be perpendicular to the board surface. Pairs of the external terminal electrodes are disposed, respectively, on the two surfaces of the chip that are perpendicular to the board surface. Thus, at the time of reflow, the Manhattan phenomenon that a chip rises up can be prevented from occurring.
Also, according to the invention, the multi-laminated inductor is made of a coil having a winding layer having a coil conductor formed and a lead layer laminated outside the turn layer, and of external terminal electrodes formed on a chip surface nearly parallel to the winding center-line of the coil and connected to the lead internal conductors. When the multi-laminated inductor described above is manufactured, by changing the position where the lead internal conductor is disposed on the insulating material sheet making up the lead layer, the position where the lead internal conductor is connected to the coil end can be changed. Thus, the multi-laminated inductor of different inductance values can be obtained.
Further, in this manufacturing method, internal conductors shaped like a letter I, L or U and via holes to be connected to the end portion thereof are formed on insulating material sheets. Then, the winding layer is formed by laminating a plurality of these insulating material sheets so that the internal conductors may form a coil. Also, the lead layer comprises one or more insulating material sheets on each of which a lead internal conductor having one end thereof connected to a coil end and the other end thereof reaching to an edge of the sheet is formed.
According to this manufacturing method of the multi-laminated inductor, by changing the position where the lead internal conductor is connected to a coil end, there is made a portion of the coil end which does not function as a coil. Thus, inductance values can be changed.
Further, in the manufacturing method described above, only changing the position to form the lead internal conductor allows a change or adjustment of the value of inductance. Therefore, at the time of manufacturing, only the preparation of insulating material sheets having the lead internal conductor formed at a varied position allows easy manufacturing of the multi-laminated chip inductors with a different value of inductance, without changing the outside shape and the position of the external terminal electrodes.
Therefore, the adjustment of an inductance value does not require extensive redesigns such as changing the core area as previously needed. Further, it is not necessary extensively to change the content of design for each different value of inductance. Thus, it is very simple to control the design specification.
Also, in the manufacturing method for the multi-laminated inductor described above, an internal conductor making up a coil end and at least a portion of a lead internal conductor are opposed and connected to each other without existence of the insulating material sheet between them. For this, an insulating material sheet having a lead internal conductor or an internal conductor making up the coil end formed thereon is laminated on the other insulating material sheet with reverse from top to bottom so that the structure described just above may be obtained.
According to this manufacturing method, when the inductance value is varied by changing the position to form the lead internal conductor, even in cases where two or more insulating material sheets require some modification such as through-hole machining, this variation is possible only by changing one insulating material sheet having the lead internal conductor formed. That is, an insulating material sheet having a lead internal conductor or an internal conductor making up the coil end formed thereon is laminated on the other insulating material sheet with reverse from top to bottom.